Hoses have been developed which are useful for Freon service in refrigeration and air conditioning systems, particularly to automobile air conditioners, wherein hoses or other suitable flexible conduit members are employed for the purpose of joining the principal operating components of the refrigerating device. These hoses should have good flexibility, high strength, the ability to bend to small radii without kinking, small outside diameter in relation to inside diameter and impermeability to the fluids involved. In addition, these refrigeration hoses are subjected to temperature extremes in under-the-hood applications, and further, must meet requirements for proper coupling attachment. Freon.TM. type fluoro-halo derivatives of aliphatic hydrocarbons are widely used in refrigeration devices because of their low toxicity and other suitable properties. However, the containment of these halogenated hydrocarbons within the refrigeration circuit has always been a problem. Hoses of conventional synthetic material such as nylon, polyvinyl chloride polymers and the like, although having characteristics suitable, are in most cases permeable to water vapor which makes them undesirable for refrigeration service. In the past, attempts have been made to solve the water vapor permeability problem by applying a covering of thin sheet material over the tube core. Such sheet material has been wrapped about the tube so as to result in a longitudinal seam or has been spirally wrapped with a resulting spiral seam and has been manufactured from such materials as Mylar.TM., Teflon.TM. Saran.TM. and polypropylene.
The sheet material is not only difficult to apply to the core tube, but may also present problems in adhering to the core tube or surrounding reinforcement and in keeping the seam tight when the core tube expands and contracts during pressure variations or when the hose is bent or flexed. A particular problem involves hose constructions wherein the sheet materials impart an undesirable rigid character to the hose such that when the hose is bent or flexed, separation of the hose components results with attendant failure of the hose.
A major portion of air conditioner hose presently employed in automobile air conditioners is a three-layer structure. The innermost tubular layer of the hose is formed of an elastomeric material intended to keep the refrigerant fluid and compressor lubricant in the hose and moisture and air out. Since the refrigeration apparatus is subject to greater than atmospheric pressures by the refrigerant, a layer of reinforcing braiding is wound upon the outside surface of the inner tube. An outer layer of elastomer resistant to ozone, engine oil and other contaminating materials likely to be present in the engine compartment is typically extruded over the braided reinforcement. In hoses of this type, the inner layer is acrylonitrile-butadiene rubber or chlorosulfonated polyethylene, the braiding fibers may be rayon and other conventional fibers, and the outer layer is neoprene or EPDM.
Even though numerous refrigerant hose designs have been developed, they fail to combine low Freon permeability, low water permeability, flexibility, vibration resistance and good coupling properties to the hose over temperature extremes.
U.S. Pat. No. 805,848 discloses a hose comprising a core tube of polyamide coated with a vinylidene chloride polymer, a tensioned reinforcement and a sheath, the reinforcement being bonded to both the coating and the sheath.
U.S. Pat. No. 3,528,260 discloses and claims refrigerant hoses formed of a major proportion of crosslinked chlorinated polyethylene. This patent discloses that a mixture of about 85 to 90 parts by weight of crosslinked, chlorinated polyethylene with 10 to 15 parts by weight of a suitable cured elastomeric material such as acrylonitrile-butadiene rubber, chlorinated butyl rubber, neoprene, chlorosulfonated polyethylene or polyepichlorohydrin is also fairly impervious to Freons and has some of the other physical and chemical properties required for use as air conditioning hose.
U.S. Pat. No. 3,266,527 discloses a hose structure comprising a tubular core of flexible material, a helically wound strip of substantially impervious plastic material concentrically, constrictively surrounding said core, a flexible layer of reinforcing braid concentrically surrounding said sheath and a flexible protective tubular jacket concentrically surrounding said braid layer. This patent discloses that the core may be formed of a polyamide, a polyolefin or a polyvinylchloride material, the sheath being preferably formed of a suitably impervious plastic material such as polyethyleneterephthalate, polyvinylidene chloride-vinylchloride copolymer, FEP fluorocarbons and the like. The sheath materials disclosed comprise a heat shrinkable material which permits facilitated positive association thereof with the tubular core.
None of the prior art suggests or discloses a hose construction wherein (1) a polyamide core of a specific thickness has bonded to it an (2) elastomeric friction layer which comprises (a) a base polymer such as EPDM, (b) a source of calcium ions, (c) an adhesion system, and (d) a peroxide curative; which is on the outer surface of the core and adhered directly to it, (3) a layer of tensioned reinforcement strands cover the elastomeric friction layer, (4) an adhesive/ barrier friction layer comprising a natural or synthetic elastomer or ethylene acrylic acid copolymers between the first and second layers of tensioned reinforcement, and finally, (5) a cover, specifically a chlorobutyl rubber cover, which uses a bis-dienophile as a crosslinker. It has been discovered that this particular construction has excellent Freon and water impermeability, and further, provides the required flex, vibration resistance and coupling properties for utilization in automotive air conditioning systems.